1. Field of the Invention
The present disclosure relates to an organic light emitting display device and a method of fabricating the same, and particularly, to an organic light emitting display device having a simple structure and reducing fabrication costs, and a method of fabricating the same.
2. Background of the Invention
Recently, various flat panel display devices capable of reducing weight and volume as shortcomings of cathode ray tubes have been developed. Such flat panel display devices include a liquid crystal display device, a field emission display device, a plasma display panel, an organic light emitting display device, etc.
Among the flat panel display devices, a plasma display has a simple structure and fabrication process, is light, thin, short, and small, and most advantageous for a large screen, and thus, it receives much attention, and it has low luminous efficiency and luminance and much power consumption. Compared to the plasma display, a liquid crystal display device uses a semiconductor process, so it is difficult to have a large screen and consumes much power due to a backlight unit. Also, a liquid crystal display makes a great light loss due to optical elements such as a polarization filter, a prism sheet, a diffusion plate, or the like, and has a narrow viewing angle.
Compared to the liquid crystal display, an organic light emitting display device is divided into an inorganic light emitting display device and an organic light emitting display device. The light emitting display device is a self-luminous device and has advantages in that it has fast response speed and high luminous efficiency and luminance, and wide viewing angle. Compared to an organic light emitting display device, an inorganic light emitting display device has high power consumption, cannot obtain high luminance, and cannot emit various colors of light. Meanwhile, an organic light emitting display device is driven with a DC voltage as low as tens of volts, has a fast response speed, obtains high luminance, and emits various colors of light such as R, G, and B, and thus, currently, it is actively researched.
However, the organic light emitting display device has the following problems. In general, it is widely known that an organic light emitting material forming an organic light emitting layer is vulnerable to moisture. That is, when moisture infiltrates into an organic light emitting layer of the organic light emitting display device, luminous efficiency of the organic light emitting material is degraded to cause a fatal defective organic light emitting display device.
In order to prevent infiltration of moisture, an anti-moisture insulating layer is formed. A conventional art organic light emitting display device including an anti-moisture insulating layer will be described briefly as follows.
FIG. 1 is a view schematically shown a structure of a conventional art organic light emitting display device.
As shown in FIG. 1, the conventional art organic light emitting display device is a top emission display device and includes a substrate 10 on which a thin film transistor (TFT) and various wirings are formed, a first electrode 20 formed on the substrate 10, an organic light emitting layer 25 formed on the first electrode 20, a second electrode 30 formed on the organic light emitting layer 25, a buffer layer 50 formed on the second electrode 30, a passivation layer 60 formed on the buffer layer 50, and a protective film 70 attached to the passivation layer 60.
The substrate 10 is a glass substrate, and a thin film transistor, and the like, is formed on the glass substrate. The first electrode 20 is an anode, and the second electrode 30 is a cathode. Thus, electrons are injected from the second electrode 30 to the organic light emitting layer 25 and holes are injected from the first electrode 20 to the organic light emitting layer 25 to form excitons in the organic light emitting layer. As the excitons decay, light corresponding to an energy difference of lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the light emitting layer is generated and output to the outside (an upward direction of the second electrode 30 in the drawing).
The buffer layer 50 and the passivation layer 60 are provided above the second electrode 30. The passivation layer 60 is a layer for blocking infiltration of moisture into the organic light emitting layer 25 from the outside, and the buffer layer 50 prevents the second electrode 30 from being damaged to cause a defect when the passivation layer 60 is formed.
In general, the passivation layer 60 is made of an inorganic material and formed through chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD). Among the processes, the CVD process is performed at a high temperature, so the second electrode 30 is affected by the high temperature during the process, causing a defect. Also, during the PECVD process, plasma particles having high energy collide with the second electrode 30 to damage the second electrode 30, causing a defective product.
The buffer layer 50 is formed to prevent the second electrode 30 from being defective during a process of forming the passivation layer 60. The buffer layer 50 is made of a high-priced organic material such as CuPc (copperpthalocyanine), PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride), BCP (Li-doped 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), and thus, when the buffer layer 50 is formed, fabrication costs are increased, and because an additional buffer layer formation process is required, the fabrication process is complicated.